Alternating current (ac) machines (e.g., IPM machines) are extensively used in loaders, combines or other heavy equipment machinery vehicle electric drive because they provide a higher efficiency than direct current (dc) machines. Of the ac machines, an Interior Permanent Magnet (IPM) machine has high drive efficiency and a wider constant power operating range. An IPM machine controller also called an inverter, controls operation of the IPM machine. The controller produces ac control signals which are applied to the terminals of the IPM machine.
In an IPM machine, a current limiting feature may be enabled such as stall current limiting and peak power. For example, a peak power feature may enable an inverter supply overload current to the machine. An overload current occurs when a current command is greater than a continuous rating of the machine.
If the peak power feature is enabled, the inverter monitors and protects the inverter during overloads. Failure to protect the inverter may result in damage to inverter components such as current sensors, DC bus capacitors and bus bars. An overload condition limit is defined along with an amount of time which overload current is allowed. The frequency for which repetitive overload conditions are allowed may also be defined. Once the inverter supplies overload current for a duration, the inverter current may then be limited for the remainder of a cycle.